Method for producing prepolymers with an isocyanate termination for producing polyurethanes

ABSTRACT

The invention relates to a method for producing a polyurethane prepolymer with an isocyanate termination, having a low content of free diisocyanates. The invention also relates to a method for producing polyurethanes, polyurethane urea or thermoplastic polyurethane granules.

FIELD OF THE INVENTION

The present invention relates to the preparation ofisocyanate-terminated polyurethane prepolymers having a freediisocyanate monomers content of less than or equal to 0.1% by mass.These isocyanate-terminated polyurethane prepolymers are useful forpreparing polyurethanes, polyurethane ureas or thermoplasticpolyurethane pellets.

BACKGROUND OF THE INVENTION

Polyurethanes count among the most polyvalent commercial materials.Thermosetting or thermoplastic, polyurethanes are used in a large numberof industries. For example, they can be used to form flexible foamsparticularly used in furnishings and in the automobile industry or rigidfoams used as insulators in building construction or electric householdappliances. Polyurethanes also enter into the composition of manyadhesives, lacquers, varnishes, paints, etc.

Many methods for preparing polyurethanes have been developed. Forexample, polyurethanes can be prepared in a single step by mixing thevarious polymer components, generally in the absence of solvent. Theycan also be prepared from isocyanate-terminated prepolymers formed byreaction between an isocyanate, typically employed in large excess, anda polyol. In this latter method, the reaction of the prepolymer with achain extender and/or a crosslinking agent leads to the formation ofpolyurethane. Polyurethane prepolymers prepared conventionally generallycontain a significant proportion of unreacted isocyanate, referred toherein as “free isocyanate”.

Isocyanates are toxic compounds. At high concentrations, they canirritate the skin and the mucous membranes. Continuous exposure to lowconcentrations can, as for it, be at the origin of a sensitizationleading to skin or respiratory allergies. Certain isocyanates even proveto be carcinogenic. Their penetration into the organism occurs mainlyvia the respiratory tract in vapor or aerosol form. Toluene diisocyanate(TDI), diphenylmethylene diisocyanate (MDI) and p-phenyl diisocyanate(PPDI) prove to be particularly noxious because of their highvolatility.

Since the coming into force of the REACH regulation of the EuropeanUnion, certain chemical substances or groups of chemical substances arefor certain uses subject to marketing and use restrictions. Inparticular, since December 2010, the marketing of products containingmore than 0.1% of free MDI or TDI is strictly regulated.

Furthermore, other than the health problems they can cause, freeisocyanates present in isocyanate-terminated prepolymers can alter theproperties of the polyurethanes formed from these prepolymers. Indeed,free isocyanates can react with chain extenders creating isolated rigidsegments at the origin of phase separation problems.

To overcome these disadvantages and to reduce health risks, efforts havebeen undertaken to reduce the free isocyanate contents inisocyanate-terminated prepolymers. Free isocyanates are generallyremoved by vacuum distillation, giving rise to substantial additionalpreparation costs.

There is thus a need to have a method for obtainingisocyanate-terminated polyurethane prepolymers having a low freediisocyanate content (less than or equal to 0.1%) at a lower cost.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a method for preparing anisocyanate-terminated polyurethane prepolymer having a free diisocyanatemonomers content of less than or equal to 0.1% by mass relative to thetotal mass of the prepolymer and having an NCO value of 2 to 6, saidmethod comprising the following steps:

-   -   a) reacting at a temperature of 20 to 70° C. with degassing:        -   i. diisocyanate monomers selected from diisocyanates having            two NCO functions having a difference in reactivity higher            than 6, said difference in reactivity resulting from the            dissymmetry of the monomers and/or from a substitution            effect;        -   ii. polyols with a functionality of 2 having a molar mass of            150 to 3000 g/mol; the diisocyanate monomers and the polyols            being in such a quantity that the ratio of “number of NCO            functions” to “number of OH functions” varies from 1.4 to 2;    -   b) degassing and stabilizing the reaction medium obtained in        step a) at a temperature of 50° C. to 110° C.;    -   c) recovering said isocyanate-terminated polyurethane        prepolymer.

The present invention also relates to the use of anisocyanate-terminated polyurethane prepolymer obtained according to thepreceding method for preparing polyurethanes by low-pressure orhigh-pressure casting, or by means of a liquid-injection machine.

The present invention also relates to the use of anisocyanate-terminated polyurethane prepolymer obtained according to thepreceding method for preparing thermoplastic pellets, in particular bymeans of an extruder with underwater pelletizing then injection in apress.

The present invention relates to a method for preparing a polyurethane,polyurethane urea or thermoplastic polyurethane (TPU) pellets,comprising the following steps:

-   -   iv) preparing an isocyanate-terminated polyurethane prepolymer        having a free diisocyanate monomers content of less than or        equal to 0.1% by mass relative to the total mass of the        prepolymer and having an NCO value of 2 to 6 according to the        preceding method;    -   v) reacting the prepolymer obtained in step iv) with polyols        or/and polyamines, said polyols and polyamines having an average        molar mass of 50 to 4000 g/mol and an average functionality        equal to or greater than 2;    -   vi) recovering said polyurethane, polyurethane urea or TPU        pellets.

Definitions

In the context of the present invention, unless otherwise specified,percentages are percentages by mass.

According to the present invention, the terms “degassing” or “degas”relate to all techniques known to the skilled person for eliminatinggases contained in the chamber in which the method for preparing apolyurethane prepolymer according to the present invention is carriedout. For example, a simple pump can be connected to evacuate gas fromthe chamber and thus to lower the gas pressure thereof. Advantageously,the chamber pressure is close to 0.5 atmosphere (±0.1 atmosphere), moreadvantageously close to 0.25 atmosphere (±0.1 atmosphere), still moreadvantageously close to 0.1 atmosphere (±0.1 atmosphere), and inparticular 0 atmosphere.

The ratio of “number of NCO functions” to “number of OH functions”according to the present invention can be determined theoretically onthe basis of the structure and quantity of the diisocyanates and polyolsinvolved. Alternatively, any assay technique for determining the numberof both NCO and OH functions is applicable.

By the term “stabilization” or “stabilizing”, for example in theexpression “stabilizing the reaction medium obtained in step a) at atemperature of 50° C. to 110° C.”, it is meant that the temperature ismaintained at a value for a determined period of time, which is besidesthe generally accepted definition of this term. Advantageously, thistemperature value can nevertheless exhibit small variations on the orderof±10° C., indeed±5° C. The stabilized temperature values can be between60 and100° C., between 70 and 90° C., between 75 and 85° C.,preferentially 80° C. The determined period in the context of thepresent invention can vary from several minutes (for example 10 minutes,20 minutes, 30 minutes or 45 minutes) to several hours (thus after onehour, indeed 2 hours, 3 hours, 5 hours, 10 hours or 15 hours). This timeperiod is a function of the technical effect disclosed in the presentpatent application, which is to limit the free isocyanates content. Thistime period is also a function of the desired yield, i.e., the optimumreaction yield. The skilled person will thus adapt this time value tothe technical effect sought.

The expression “molar mass” in the context of the present inventionrelates to the mass average molar mass (also referred to as “by weight”)according to the general definition the skilled person can apply:

${\overset{\_}{M}}_{w} = {\frac{\Sigma_{i}m_{i} \times M_{i}}{\Sigma_{i}m_{i}} = \frac{\Sigma_{i}N_{i} \times M_{i}^{2}}{\Sigma_{i}N_{i} \times M_{i}}}$

Any technique known in the art for determining this average molar massis applicable to the present invention, for example by dynamic lightscattering, ultracentrifugation, mass spectrometry (e.g., MALDI-TOF), orby any applicable chromatography technique such as exclusion (alsoreferred to as “size exclusion”) or on permeable gel.

Viscosity, as the skilled person well knows, expresses, in short, afluid's resistance to flow. Viscosity can be measured by any techniqueknown by the skilled person at the selected temperature. For example, inthe context of the present invention, it is possible to use aBrookfield-type viscometer at the selected temperature. Advantageously,the viscosity of the isocyanate-terminated polyurethane prepolymer islower than 6000 mPa·s at a temperature between 85° C. and 105° C.,preferentially 95° C.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have shown that isocyanate-terminated polyurethaneprepolymers having a free diisocyanate monomers content of less than orequal to 0.1% by mass relative to the total mass of the prepolymer andhaving an NCO value of 2 to 6 could be prepared by a method comprisingthe following steps:

-   -   a) reacting at a temperature of 20 to 70° C. with degassing:        -   i. diisocyanate monomers selected from diisocyanates having            two NCO functions having a difference in reactivity higher            than 6, the difference in reactivity resulting from the            dissymmetry of the monomers and/or from a substitution            effect;        -   ii. polyols with a functionality of 2 having a molar mass of            150 to 3000 g/mol; the diisocyanate monomers and the polyols            being in such a quantity that the ratio of “number of NCO            functions” to “number of OH functions” varies from 1.4 to 2;    -   b) degassing and stabilizing the reaction medium obtained in        step a) at a temperature of 50° C. to 110° C.;    -   c) recovering said isocyanate-terminated polyurethane        prepolymer.

Advantageously, the method developed by the inventors does not include adistillation step. Thus, the isocyanate-terminated polyurethaneprepolymer is recovered directly after carrying out steps a) and b).

The NCO value of the isocyanate-terminated polyurethane prepolymers is ameasured value. It can be determined by assay according to the standardNF T52 132.

The NCO value of the isocyanate-terminated polyurethane prepolymersvaries from 2 to 6. More particularly, the NCO value of theisocyanate-terminated polyurethane prepolymers can vary from 2.2 to 5.3.

The free diisocyanate monomers content in the isocyanate-terminatedpolyurethane prepolymers can be determined by gas chromatographyaccording to the standard NF EN ISO 10283.

The diisocyanate monomers are selected from diisocyanates having two NCOgroups having a difference in reactivity higher than 6, the differencein reactivity resulting from the dissymmetry of the monomers and/or froma substitution effect. This difference in reactivity is given in thescientific literature (Pascault et al., “Thermosetting Polymers” Ed. M.Dekker, 2002, Chap. 2 page 18: “The reactivity of diisocyanates is welldocumented in the literature. For symmetric diisocyanates such asdiphenylmethane 4,4′-diisocyanate (MDI) or para-phenylene4,4′-diisocyanate (PPDI), both NCO groups have initially the samereactivity. But as the NCO group itself exhibits an activating effect onisocyanate reactivity, the fact that one NCO group has reactedintroduces a substitution effect that usually decreases the reactivityof the second NCO group.

This effect is more pronounced in PPDI than in MDI; the ratio of therate constants for the reaction with an aliphatic alcohol is k₁/k₂=9 andk₁/k₂=2, respectively (at room temperature).

Asymmetric diisocyanates such as 2,4-TDI are more complex because theinitial reactivity of the two isocyanate groups is not equivalent andthe substitution effect amplifies the difference. The 4-NCO is about10-20 times more reactive than the 2-NCO, but the reactivity ratio alsodepends on temperature (see Chapter 5). This difference also explainswhy the TDI dimer can be prepared quantitatively (Eq. 2.28).”).

Consequently, it is clear that the term “reactivity” employed in thepresent invention corresponds to the reaction rate of an NCO group withan OH group and the “difference in reactivity” is the ratio of thereaction rates between the first NCO group and the second NCO groupwhich react with a polyol.

Reaction of the first NCO group: V₁=k₁[NCO₁][OH]

Reaction of the second NCO group: V₂=k₂[NCO₂][OH]

and V₁/V₂=k₁/k₂.

Preferably, the difference in reactivity is higher than 8.

When the difference in reactivity results from a substitution effect,the diisocyanate monomers can be symmetrical molecules having two NCOgroups of equal reactivity. When one of these NCO groups reacts, asubstitution effect is produced which usually decreases the reactivityof the second NCO group.

The diisocyanate monomers can be aliphatic, aromatic or cycloaliphatic.Preferably, the diisocyanate monomers are aromatic. More particularly,the diisocyanate monomers can be selected from the group comprisingtoluene-2,4-diisocyanate (2,4 TDI), 1,4-phenylene diisocyanate (PPDI)and a mixture thereof.

The polyols used in the method for preparing prepolymers have afunctionality of 2 and a molar mass of 150 to 3000 g/mol, preferably 250to 3000 g/mol or 250 to 2000 g/mol. The functionality of the polyolrefers to the number of hydroxyl groups per molecule. Such polyols arewell-known to the skilled person.

The polyols can be selected from the group comprising polyesters,polyethers, polycarbonates, polyolefins and mixtures thereof.

More particularly, the polyols can be selected from the group comprisingpolymers of 1-2 propylene glycol, of 1-3 propylene glycol, of ethyleneglycol, of butylene glycol, polycaprolactones, polytetramethyleneglycols, polyolefins of the polybutadiene and hydrogenated polybutadienetype, polyols derived from fatty acids and vegetable oils, such oilsderived from colza, castor oil plants, soya, and mixtures thereof.

In certain embodiments of the present invention, the diisocyanatemonomers and the polyols are selected from the following combinations:

-   -   1,4-phenylene diisocyanate and/or toluene-2,4-diisocyanate and        polycaprolactones;    -   1,4-phenylene diisocyanate and/or toluene-2,4-diisocyanate and        polyethers;    -   1,4-phenylene diisocyanate and/or toluene-2,4-diisocyanate and        polyolefins of vegetable origin.

The diisocyanate monomers and the polyols are in such a quantity thatthe ratio of “number of NCO functions” to “number of OH functions”varies from 1.4 to 2, preferably from 1.45 to 1.65.

The reaction between the diisocyanate monomers and the polyols accordingto step a) of the method of the present invention is typically carriedout in the absence of catalyst and/or under vacuum. Step a) is carriedout at a temperature of 20 to 70° C., indeed 20° C. to 60° C.

The viscosity of the product of the reaction between the diisocyanatemonomers and the polyols is controlled by the temperature, the NCO/OHratio and the molar masses of the polyols. The skilled person will beable to adapt these parameters in such a way that the viscosity of theproduct obtained in step a) does not exceed 6000 mPa·s at the selectedtemperature.

The stabilization of the product resulting from step a) is carried outat a temperature of 50° C. to 110° C., preferably 65° C. to 100° C.Stabilization is preferably carried out under vacuum. Generally, stepsa) and b) (combined) are carried out with stirring for at least 15hours.

The isocyanate-terminated polyurethane prepolymers obtained by themethod of the present invention can be used to prepare polyurethanes orpolyurethane ureas. They can also be used to prepare TPU pellets.Polyurethanes or polyurethane ureas can be prepared by low-pressure orhigh-pressure casting or by means of a liquid-injection machine. TPUpellets can be prepared by means of an extruder, in particular anextruder with underwater pelletizing then injection in a press.

Thus, the present invention also relates to a method for preparing apolyurethane, polyurethane urea or TPU pellets comprising the followingsteps:

-   -   iv) preparing an isocyanate-terminated polyurethane prepolymer        having a free diisocyanate monomers content of less than or        equal to 0.1% by mass and having an NCO value of 2 to 6        according to the method described above;    -   v) reacting the prepolymer obtained in step iv) with polyols        or/and polyamines of average molar mass of 50 to 4000 g/mol, and        average functionality equal to or greater than 2;    -   vi) recovering said polyurethane, polyurethane urea or TPU        pellets.

The polyols or amines of average functionality equal to 2 are generallyreferred to by the term “chain extenders”. Chain extenders can bealiphatic or aromatic.

Examples of chain extenders include diols, such as for example ethyleneglycol, 1,4-butanediol, 1,3-propanediol, hydroquinonebis(2-hydroxyethyl)ether, isosorbide and isomers thereof or polyethers,polycaprolactones, polyesters, polycarbonates, polyolefins and polyolsderived from fatty acids or vegetable oils as described above andmixtures thereof.

Examples of chain extenders include diamines, such as for example6-methyl-2,4-bis(methylthio)phenylene-1,3-diamine,3,5-diethyltoluene-2,4-diamine, 4,4-methylenebis(3-chloro-2,6-diethylaniline) and mixtures thereof.

The polyols or amines of average functionality higher than 2 aregenerally referred to by the term “crosslinking agents”. Examples ofcrosslinking agents include glycerol, sorbitol, trimethylolpropane andcastor oil.

The polyols or/and polyamines useful in step v) of the method have anaverage molar mass of 50 to 4000 g/mol, preferably 50 to 500 g/mol andeven more preferably 50 to 250 g/mol.

Monoalcohols and/or monoamines serving as chain limiters can also beadded to the polyols or/and polyamines of step v). Examples of chainlimiters include 1-(2-aminoethyl)-2-imidazolidinone or UDETA (Reverlink®FA from Arkema) and 2-morpholino ethylamine.

The polyurethanes obtained by the method described above are free ofisolated rigid segments. The absence of isolated rigid segments makespossible the use of monofunctional chain limiters able to createsupramolecular bonds.

In certain embodiments, the prepolymer is obtained by reaction between1,4-phenylene diisocyanate and a polycaprolactone, and the chainextender is hydroquinone bis(2-hydroxyethyl)ether or 1,4-butanediol.

In other embodiments, the prepolymer is obtained by reaction between1,4-phenylene diisocyanate and a polyether, and the chain extender is1,4-butanediol.

The components necessary to step iv) and v) can be introduced into anextruder, such as a twin-screw extruder, to prepare thermoplasticpolyurethane (TPU) pellets.

The present invention also relates to a method for preparingthermoplastic polyurethane pellets comprising the mixing of anisocyanate-terminated polyurethane prepolymer obtained according to themethod described above with a chain extender having a functionality of 2in an extruder coupled to an underwater pelletizer.

The polyurethane elastomers and the TPU obtained by the method of thepresent invention have properties at least equivalent, if not superiorto polyurethanes prepared from isocyanate-terminated polyurethaneprepolymer the preparation of which includes a distillation step. Inparticular, the polyurethanes have excellent mechanical and chemicalproperties:

-   -   Resistance to solvents, fluids and hydrolysis;    -   Resistance to abrasion, tearing and cutting;    -   Compression set, Resilience;    -   Excellent behavior under UV and at high temperatures;    -   Excellent isotropy properties;    -   Barrier and acoustic properties.

EXAMPLES

Preparation of Isocyanate-Terminated Polyurethane Prepolymers

TABLE 1 The following isocyanate-terminated polyurethane prepolymerswere prepared: Formulation Parts by weight Prepolymer 1 Prepolymer 2Prepolymer 3 Prepolymer 4 Prepolymer 5 Diisocyanate TDI 100 TDI 100 TDI100 PPDI PPDI 34.4 12.93 29.22 14.116 16.7 Polyol¹ Terathane 250 RADIA7282 PRIPOL 2033 CAPA 2201A CAPA 2201A 11.75 87.07 53.92 77.341 23.32Polyol¹ Terathane 650 — RADIA 7282 CAPA 2043 CAPA 2101A 53.15 16.868.543 59.71 Antioxidant Ethanox 310 — — — Irganox 1010/ 0.7 Irgafos 1680.09/0.18 Theoretical 5.74 2.45 5.00 2.30 2.72 NCO value NCO² value 5.222.29 4.69 2.20 2.52 Viscosity³ 2500 mPa · s at 3670 mPa · s at 1850 mPa· s at 4900 mPa · s at 5000 mPa · s at 80° C. 85° C. 85° C. 100° C. 85°C. Tg −32.5° C. −48.3° C. −17.2° C. −44.0° C. −40.0° C. Free 0.04% 0.04%0.09% 0.088% 0.1% diisocyanate content⁴ ¹Polyol with a functionality of2 ²Measured according to the standard NF T52 132 ³Measured by means of aLAMY TVe-05 viscometer ⁴Measured according to the standard NF EN ISO10283

The TDI 100 and the PPDI are as provided by VENCOREX, France and DKSH,France, respectively.

The polyols used are provided by:

-   -   Perstorp (CAPA™ 2043, CAPA™ 2201A, CAPA™ 2101A)    -   Invista (Terathane® 250, Terathane® 650)    -   Croda (PRIPOL™ 2033)    -   Novance/Oleon (RADIA 7282)

TABLE 2 Perstorp CAPA 2043 POLYCAPROLACTONE SpecificationsCharacteristics Units Result Minimum Maximum Hydroxyl value mg/g282.8000 mg/g 265 295 (KOH) Acid value mg/g 0.0800 mg/g — 0.25 (KOH)Water % (m) 0.0150% (m) — 0.020 Color Hazen 20 Hazen — 50Clearness-clear — CONF  0 0 liquid gloss

TABLE 3 Perstorp CAPA 2101A POLYCAPROLACTONE SpecificationsCharacteristics Units Result Minimum Maximum Hydroxyl value mg/g113.0000 mg/g 108 116 (KOH) Acid value mg/g 0.0200 mg/g — 0.05 (KOH)Water % (m) 0.0100% (m) — 0.020 Color Hazen <10 Hazen — 20

TABLE 4 Perstorp CAPA 2201A POLYCAPROLACTONE SpecificationsCharacteristics Units Result Minimum Maximum Hydroxyl value mg/g 57.1000mg/g 54.0 58.0 (KOH) Acid value mg/g 0.0200 mg/g — 0.05 (KOH) Water %(m) 0.0150% (m) — 0.020 Color Hazen <20 Hazen — 50

TABLE 5 TETRATANE ® 250 Molecular mass 255 230-270 Color (APHA) Hazen 14Max. 40  Water ppm 78 Max. 150 Alkalinity number MeqOH/30 kg −1.01−2.0-+1.0 Hydroxyl number 440.0 488-416

TABLE 6 TETRATANE ® 650 Product properties Batch analysis MinimumMaximum Molecular mass 658 625 675 Color (APHA) Hazen 20 0 50 Water ppm66 0 150 Alkalinity MeqOH/30 kg −0.62 −2.00 1.00 number Hydroxyl 170.5166.2 179.5 number

TABLE 7 TETRATANE ® 2000 Product properties Batch analysis MinimumMaximum Molecular mass 2027 1900 2100 Color (APHA) Hazen 11 0 40 Waterppm 49 0 150 Alkalinity MeqOH/30 kg −0.91 −2.00 1.00 number Hydroxyl55.4 53.4 59.1 number

TABLE 8 CRODA PRIPOL 2033-LQ-(GD) Method Standards Results no. AnalysisMini Maxi Unit value Units Conformity ADDEND00 CONFORMS CONFORMS — P Y/NAAF00000 Revision number 20.0 CONFORMS — P EF100100 ACID VALUE 0.00 0.200.05 mg/KOH/g P EF100700 SAPONIFICATION 0.0 2.0 0.4 mg/KOH/g P VALUEEF100200 HYDROXYL 202 212 210 mg/KOH/g P VALUE LF100600 APHA COLOR 0 505 Hazen P EF100300 WATER 0.00 0.10 0.07 % P LF934100 MONOMER 0.0 2.0 0.5% P ALCOHOL LF934100 DIMER INCL. 1.5- 96.5 100.0 98.7 % P MER ALCOHOLLF934100 TRIMER 0.0 1.5 0.8 % P ALCOHOL

TABLE 9 Oleon: Radia 7282 Analysis results Units Result Min. Max. MethodAcid value Mg KOH/g 0.70 0.00 1.00 AOCS cd 3d-63 Water % (m) 0.01 0.000.10 AOCS Ca 2^(nd)-84 Hydroxyl 57.9 52.0 60.0 Novance A76 valueViscosity at 26.8 25.0 35.0 Novance B326 40° C.

Preparation of Prepolymer 1

Preparation of the Polyols Mixture

TERATHANE 250 and then TERATHANE 650 are loaded into a tank. The mixtureis placed at 100° C. with vigorous stirring (195 rpm) under vacuum. Themixture of TERATHANE 250 and ETHANOX 310, first melted in an oven at125° C. with stirring, is then added. The mixture is then stabilized for17 hours under vacuum at 41° C. with stirring at 70 rpm.

Preparation of the Prepolymer

Liquid TDI is introduced from the top into a reactor tank at 27±3° C.The homogeneous mixture of polyols at 41±1° C. is introduced by pumpingfrom the bottom with stirring at 70 rpm. When all the polyols mixture ispumped in, stirring is increased to 235 rpm. The whole is then subjectedto a vacuum. During the exothermic phase, the setpoint temperature ofthe tank is controlled so that the temperature of the mixture does notexceed 60±5° C. and then the product is stabilized at 65±2° C. The wholeis then stirred for at least 15 hours under vacuum at 215 rpm at 65° C.The product obtained is then stabilized for 2 hours at 80° C. anddegassed.

Preparation of Prepolymer 2

Liquid TDI is introduced from the top into a reactor tank at 27±3° C.The polyol at 55±1° C. is introduced by pumping from the bottom withstirring at 70 rpm. When all the polyols mixture is pumped in, stirringis increased to 235 rpm. The whole is subjected to a vacuum. During theexothermic phase, the setpoint temperature of the tank is controlled sothat the temperature of the mixture does not exceed 60±5° C. and thenthe product is stabilized at 65±2° C. The whole is stirred at 215 rpmunder vacuum for at least 15 hours. The product is then stabilized for 2hours at 80° C. and degassed.

Preparation of Prepolymer 3

Preparation of the Mixture of RADIA 7282 and PRIPOL 2033

PRIPOL 2033 and then RADIA 7282 are loaded into a tank placed at 90°C.-100° C. The mixture is brought up to 100° C. with stirring at 195 rpmunder vacuum. The mixture is stabilized for 12 hours to maintain thepolyols at 53±1° C.

Preparation of the Prepolymer

Liquid TDI is introduced from the top into a reactor tank at 27±3° C.The homogeneous polyols mixture at 53±1° C. is introduced by pumpingfrom the bottom with stirring at 70 rpm. When all the polyols mixture ispumped in, stirring is increased to 235 rpm. The whole is subjected to avacuum. During the exothermic phase, the setpoint temperature of thetank is controlled so that the temperature of the mixture does notexceed 60±5° C. and then the product is stabilized at 65±2° C. The wholeis stirred at 215 rpm under vacuum for at least 15 hours. The product isthen stabilized for 2 hours at 80° C. and degassed.

Preparation of Prepolymer 4

Preparation of the Mixture of CAPA 2201A and CAPA 2043

CAPA 2043 and then CAPA 2201A are loaded into a tank placed at 90°C.-100° C. The mixture is brought up to 100° C. with stirring at 195 rpmunder vacuum. The mixture is stabilized for 12 hours to maintain thepolyols at 45±1° C.

Preparation of the Prepolymer

PPDI in straw form is introduced from the top into a reactor tank at45±1° C. The homogeneous polyols mixture at 45±1° C. is introduced bypumping from the top with stirring at 70 rpm. When all the polyolsmixture is pumped in and all the PPDI wetted, stirring is increased to230 rpm. The whole is subjected to a vacuum. After the exothermic phase,the product is stabilized at 65±2° C. The whole is stirred at 195 rpmunder vacuum for at least 15 hours. The product is then stabilized for 2hours at 80° C., and brought up to 100° C. under vacuum to degas it.

Preparation of Prepolymer 5

Preparation of the Mixture of CAPA 2201A and CAPA 2101A

CAPA 2101A and then CAPA 2201A are loaded into a tank placed at 90°C.-100° C. The mixture is brought up to 100° C. with stirring at 195 rpmunder vacuum. The mixture is stabilized for 12 hours to maintain thepolyols at 46±1° C.

Preparation of the Prepolymer

PPDI in straw form is introduced from the top into a reactor tank at46±1° C. The homogeneous polyols mixture at 46±1° C. is introduced bypumping from the top with stirring at 70 rpm. When all the polyolsmixture is pumped in and all the PPDI wetted, stirring is increased to150 rpm and the whole is subjected to a vacuum. After the exothermicphase, the product is stabilized at 65±2° C. The whole is stirred at 215rpm under vacuum for at least 15 hours. The product is then stabilizedfor 2 hours at 80° C., and brought up to 100° C. under vacuum to degasit.

Preparation of Polyurethane Elastomers

TABLE 10 The following polyurethanes were prepared: Composition Parts byweight PolyU 1 PolyU 2 PolyU 3 PolyU 4 PoIyU 5 Prepolymer Prepolymer 1Prepolymer 1 Prepolymer 2 Prepolymer 3 Prepolymer 4 100 100 100 100 100Extender Ethacure 300 MCDEA Ethacure 300 2-Morpholino BDO 12.8 19.6 5.46ethylamine 2.247 5.21 Extender — TERA 2000 — Polycin D-4000 — 15.0059.06 Extender — — — Ethacure 300 — 4.00 Curing 16 h 16 h 16 h 16 h 16 hTps ant T° C. 100° C. 130° C. 100° C. 130° C. 130° C.

The polyurethanes are prepared by methods well-known to the skilledperson.

The chain extenders used are provided by:

-   -   Albermarle (Ethacure 300)    -   Aceto (MCDEA)    -   Invista (Terathane 2000)    -   Sigma Aldrich (2-morpholinoethylamine)    -   Vertellus (Polycin D-4000)    -   BASF (BDO)

TABLE 11 3208 ETHACURE 300/DR 55 C/Z00001 Upper Characteristics UnitsValue Lower limit limit Method Water % weight 0.01 — 0.08 Amine value529 526 536 Color 8 — 13 (Gardner) Total diamines % weight 99.8 99.0 —

TABLE 12 ACETO FRANCE SAS, 4,4-METHYLENE BIS(3-CHLORO-2,6-DIETHYLANILINE) SPECIFICATIONS RESULTS Appearance White to off-whitepellets Conforms Purity 97% min  98.7% Water content 0.15% max 0.043%Melting point 87.0-89.0° C. 87.4-89.0° C.

TABLE 13 TETRATANE ® 2000 Batch Product properties analysis MinimumMaximum Molecular mass 2027 1900 2100 Color (APHA) Hazen 11 0 40 Waterppm 49 0 150 Alkalinity value MeqOH/30 kg −0.91 −2.00 1.00 Hydroxylvalue 55.4 53.4 59.1

TABLE 14 BASF, BDO, 1,4-Butanediol Test characteristics ResultsSpecification Test method Test % 99.729 >=99.500 GC 2-Methylbutane- %0.083 <=0.400 GC 1,4-diol Acetal % 0.091 <=0.150 GC Water ppm 43 <=200DIN 51 777 Color APHA 4 <=7 DIN EN 1567

Preparation of polyU 1

The prepolymer at 80° C. and the chain extender at 40° C. are mixed.

The curing time and temperature are as indicated in the table above.

Preparation of polyU 2

The prepolymer at 85° C. and the extenders at 95° C. are mixed.

The curing time and temperature are as indicated in the table above.

Preparation of polyU 3

The prepolymer at 80-85° C. and the extender at 40° C. are mixed.

The curing time and temperature are as indicated in the table above.

Preparation of polyU 4

The prepolymer at 95-100° C. and the extenders at 95-100° C. are mixed.

The curing time and temperature are as indicated in the table above.

Preparation of polyU 5

The prepolymer at 85-90° C. and the extender at room temperature aremixed.

The curing time and temperature are as indicated in the table above.

TABLE 15 Properties of the polyurethanes obtained Polyurethane PolyU 1PolyU 2 PolyU 3 PolyU 4 PolyU 5 Pot life¹ 2 min 30 1 min 30 3 min 12 min6-7 min Tg −21.3° C. −36.1 −51.0° C. −34.3° C. −50.2° C. Hardness² 97 9782 — 94 (Shore A) Tensile strength³ 50.9 52 27.7 2.59 37 (Mpa)Elongation at break⁴ 280 360 575 450 590 (%) Resistance to tear 123 11548.4 — 82.9 propagation⁵ (kN/m) Compression set 27 30 28 — 48 25%⁶ 22h-70° C. Water uptake 1.8% 1.9% 0.6% — 1.6% 72 hours 80° C. Adhesionafter cutting — — — 37%-1 hour — 50%-1 night ¹Time after which the mixedproduct cannot be cast ²Measured according to the standard ISO 868³Measured according to the standard ISO 37 (Determination of tensilestress-strain properties) ⁴Measured according to the standard ISO 37(Determination of tensile stress-strain properties) ⁵Measured accordingto the standard ISO 34-1 (Determination of tear strength) ⁶Measuredaccording to the standard ISO 815 (Determination of compression set)

Preparation of Thermoplastic Polyurethane Pellets

Preparation of TPU 1

The prepolymer at 90° C.-130° C. and the chain extender at 130° C. aremixed in a twin-screw extruder including several heated zones attemperatures between 200° C. and 280° C. TPU pellets are obtained byunderwater pelletizing using blades. The pellets are dried for 2 hoursat 80-110° C.

These pellets end by being injected in a press.

TABLE 16 Preparation of TPU 1 Composition Parts by weight TPU 1Prepolymer Prepolymer 5 100 Extender HQEE⁶ 5.5 Hardness¹ (Shore A) 88Tensile strength² 45 (Mpa) Elongation at break³ 590 (%) Resistance totear propagation⁴ 91 (kN/m) Compression set 25%⁵ 22 h-70° C. 14 22h-100° C. 26 ¹Measured according to the standard ISO 868 ²Measuredaccording to the standard ISO 37 (Determination of tensile stress-strainproperties) ³Measured according to the standard ISO 37 (Determination oftensile stress-strain properties) ⁴Measured according to the standardISO 34-1 (Determination of tear strength) ⁵Measured according to thestandard ISO 815 (Determination of compression set) ⁶Provided by thecompany Monument Chemical.

1. Method for preparing an isocyanate-terminated polyurethane prepolymerhaving a free diisocyanate monomers content of less than or equal to0.1% by mass and having an NCO value of 2 to 6, said method comprisingthe following steps: a) reacting at a temperature of 20 to 70° C. withdegassing: i. diisocyanate monomers selected from diisocyanates havingtwo NCO groups having a difference in reactivity higher than 6, saiddifference in reactivity resulting from the dissymmetry of the monomersand/or from a substitution effect; ii. polyols with a functionality of 2having an average molar mass of 150 to 3000 g/mol; the diisocyanatemonomers and the polyols being in such a quantity that the ratio of“number of NCO functions” to “number of OH functions” varies from 1.4 to2; b) degassing and stabilizing the reaction medium obtained in step a)at a temperature of 50° C. to 110° C.; c) recovering saidisocyanate-terminated polyurethane prepolymer.
 2. Method according toclaim 1, wherein the viscosity of the isocyanate-terminated polyurethaneprepolymer is lower than 6000 mPa·s.
 3. Method according to claim 1wherein the diisocyanate monomers are selected from the group comprisingtoluene-2,4-diisocyanate, 1,4-phenylene diisocyanate and a mixturethereof.
 4. Method according to claim 1, wherein the polyols areselected from the group comprising polyesters, polyethers,polycarbonates, polyolefins and mixtures thereof.
 5. Method according toclaim 4, wherein the polyols are selected from the group comprisingpolymers of 1-2 propylene glycol, of 1-3 propylene glycol, of ethyleneglycol, of butylene glycol, polycaprolactones, polytetramethyleneglycols, polybutadienes, hydrogenated polybutadienes, polyols derivedfrom fatty acids and vegetable oils and mixtures thereof.
 6. Methodaccording to claim 1, wherein the diisocyanate monomers and polyols areselected from the following combinations: 1,4-phenylene diisocyanateand/or toluene-2,4-diisocyanate and polycaprolactones; 1,4-phenylenediisocyanate and/or toluene-2,4-diisocyanate and polyethers; or1,4-phenylene diisocyanate and/or toluene-2,4-diisocyanate andpolyolefins of vegetable origin.
 7. Method according to claim 1, whereinstep a) is carried out in the absence of catalyst.
 8. Method accordingto claim 1, wherein steps a) and b) are carried out under vacuum and/orwith stirring for at least 15 hours.
 9. Method for preparing apolyurethane, said polyurethanes being prepared by low-pressure orhigh-pressure casting or a liquid-injection machine, or for preparingthermoplastic polyurethane (TPU) pellets using an isocyanate-terminatedpolyurethane prepolymer obtained according to the method of claim
 1. 10.Method for preparing a polyurethane, polyurethane urea or thermoplasticpolyurethane (TPU) pellets comprising the following steps: iv) preparingan isocyanate-terminated polyurethane prepolymer having a freediisocyanate monomers content of less than or equal to 0.1% by mass andhaving an NCO value of 2 to 6 according to the method of claim 1; v)reacting the prepolymer obtained in step iv) with polyols or/andpolyamines, said polyols and polyamines having an average molar mass of50 to 4000 g/mol and an average functionality equal to or greater than2; vi) recovering said polyurethane, polyurethane urea or TPU pellets.11. Method according to claim 10, wherein step v) further comprisesreaction with a monofunctional chain limiter.
 12. Method according toclaim 10, wherein the polyols are selected from the group comprisingethylene glycol, 1,4-butanediol, 1,3-propane diol, hydroquinonebis(2-hydroxyethyl)ether, isosorbide and isomers thereof, polyethers,polycaprolactones and polyols derived from fatty acids or vegetableoils.
 13. Method according to claim 10, wherein the polyamines areselected from the group comprising6-methyl-2,4-bis(methylthio)phenylene-1,3-diamine,3,5-diethyltoluene-2,4-diamine, and 4,4-methylenebis(3-chloro-2,6-diethylaniline).
 14. Method for preparing thermoplasticpolyurethane pellets comprising the mixing of an isocyanate-terminatedpolyurethane prepolymer obtained according to the method of claim 1 witha chain extender having a functionality of 2 in an extruder coupled toan underwater pelletizer.